Abstract

Nasopharyngeal cancer lies in the upper part of throat behind the nose and near the base of the skull called the nasopharynx. It is more commonly diagnosed in parts of Asia, particularly in the southern China. Five local edible plants from different families; namely curry leaf (Murraya koenigii), temu kunci (Boesenbergia rotunda), spring onion leaf (Allium cepa), mushroom bean (Phaseolus vulgaris) and bunga kantan (Phaeomeria imperialis) were macerated to obtain methanol, ethyl acetate and hexane crude extracts. Each crude extract was tested against nasopharyngeal carcinoma (HK-1) and normal nasopharyngeal epithelial (NP-69) cell lines. All crude extracts from temu kunci (Boesenbergia rotunda) were found to contain flavonoids, alkaloids and polyphenols. Both methanolic and hexane crude extracts were found to exhibit cytotoxic effects against HK-1 cells but non-toxic against NP-69 cell line. Of all the bioactive compounds previously extracted from B. Rotunda, we have selected four commercially available flavonoids and polyphenols to narrow down our search to one potential anticancer agent. These compounds were tested against HK-1 and NP-69 cell lines for cytotoxicity and it was found that cardamonin exhibits highest cytotoxic effect against HK-1 cells with IC50 of 22 μg/mL.

Cardamonin, a naturally occurring chalcone from the rhizome of Boesenbergia rotunda (locally known as temu kunci) was found to induce apoptosis in human nasopharyngeal carcinoma (HK-1) cell line in vitro. It exhibits a significant cytotoxic effect against human nasopharyngeal carcinoma cell line without affecting normal immortalized nasopharyngeal epithelial cell line (NP-69) in MTT assay. Based on these results, HK-1 cell line was treated with IC50 22 μg/mL in time-dependent manner 24, 48 and 72 hrs to further investigate the mechanisms of apoptosis. Apoptotic cells induced by cardamonin were illustrated by change in cellular morphology, increase in G2/M phase population and DNA fragmentation. Furthermore, up-regulation of caspase-3 and caspase-8 activities substantiated the induction of apoptosis through caspase-dependent pathway. Cardamonin leads to a decrease in overproduction of reactive oxygen species (ROS), disruption in mitochondrial membrane potential and drop in intracellular ATP level in HK-1 cells. Present study also revealed up-regulation of pro-apoptotic protein, Bax and apoptotic signalling factor, cytochrome c resulting in down-regulation of anti-apoptotic protein, Bcl-2. There was no fold change in caspase-9 gene expression level suggesting that HK-1 cellular apoptosis occurred independent of caspase-9. Activation of caspase-3 was directly regulated by caspase-8 and does not require caspase-9. Current findings on the mode of actions of cardamonin suggested its potential application as an anticancer agent against nasopharyngeal carcinoma.